1. Field of the Invention
The present invention relates to a system and a method for detecting an array of light spots and especially for allowing high throughput detection of multiple spots that involves spot spatial distortion correction. The array of spots is usually utilized for inspecting an article such as but not limited to a wafer, a reticle and the like.
2. Description of the Related Art
The inspection of semiconductor wafers is typically performed by scanning a laser beam across a wafer's surface and collecting light scattered therefrom. The scanning operation is conducted by scanning the laser beam across the wafer surface in a first direction using one of a variety of known deflectors, such as acousto-optic deflectors or electromechanical deflectors, while moving a stage that supports the wafer thereon in a second direction, which is typically orthogonal to the first direction. Another type of inspection includes illuminating an area and acquiring an image. U.S. Pat. No. 5,699,477 of Alumot et al, U.S patent as well of U.S. Pat. No. 6,693,664 of Neumann provide examples of such inspection systems.
There is a greater emphasis on the throughput of inspection devices and accordingly on the throughput of scanners, as the design rules for semiconductors rapidly shrink without a corresponding decrease of the inspection sequence time period or the overall size of semiconductor dies or wafers.
High throughput inspection systems utilizes optical beam arrays as well as electron beam arrays for increasing throughput. Hybrid systems that include electron beam illumination, electro-optical conversion and light beam detection are also known. Electron beams also provide higher resolution. U.S. Pat. No. 6,671,042 of Almogy, U.S. Pat. No. 6,639,201 of Almogy et al., U.S. Pat. Nos. 6,578,961 and 6,208,411 of Vaez-Iravani, U.S. Pat. No. 6,248,988 of Krantz, which are incorporated herein by reference, describe state of the art inspection systems.
The beams that form a beam array may be spatially distorted during the illumination as well as during the collection/detection stages of the article inspection process. Different beams may be distorted in a different manner. Furthermore, the distortion can change over time.
Various image processing methods are known in the art. They include die-to-die comparison, cell-to-cell comparison and die to database comparison. These comparisons require knowledge of the location of obtained pixels. In other words, spatial distortions can result in a comparison between pixels from different locations of compared dies of cells.
There is a need for a system and method for compensating for spatial distortions.